氮掺杂活性炭的制备及其吸附金-硫代硫酸根配离子的动力学研究

Preparation of Nitrogen-doped Activated Carbon and Its Kinetic on Adsorption of Gold-Thiosulfate Complex Ions

针对浸出液中金-硫代硫酸根配离子(Au(S_(2)O_(3))_(2)^(3-))难以被活性炭吸附问题,研究了以椰壳活性炭为原料,三聚氰胺为氮源,采用热活化氮掺杂法制备改性活性炭(AC-N)。考察了浸出液初始pH、吸附时间、吸附温度、初始金质量浓度、Na_(2)S_(2)O_(3)浓度、S_(4)O_(6)^(2-)浓度和主要金属离子对AC-N吸附Au(S_(2)O_(3))_(2)^(3-)的影响。结果表明:AC-N对Au(S_(2)O_(3))_(2)^(3-)吸附量随pH和温度升高呈先升高后下降趋势,随初始金质量浓度增大呈先升高后降低又升高趋势,在初始金质量浓度为20 mg/L条件下,Au(S_(2)O_(3))_(2)^(3-)吸附量达最大;Na_(2)S_(2)O_(3)易氧化分解,其产物S_(4)O_(6)^(2-)对金有钝化作用,Na_(2)S_(2)O_(3)浓度增大会抑制AC-N对Au(S_(2)O_(3))_(2)^(3-)的吸附;随共存金属离子Cu^(2+)、Pb^(2+)和Zn^(2+)质量浓度增大,Au(S_(2)O_(3))_(2)^(3-)吸附量呈先升高后下降趋势,有NH_(3)存在时,NH_(3)可与Cu^(2+)形成Cu(NH_(3))_(4)^(2+),减少Na_(2)S_(2)O_(3)消耗。吸附动力学结果表明,AC-N对Au(S_(2)O_(3))_(2)^(3-)的吸附速率先快后慢,30 h后吸附达饱和状态,吸附过程符合准一级动力学模型,吸附速率受表面液膜扩散和颗粒内扩散共同控制。

In order to solve the problem that the gold-thiosulfate complex ions in the leaching solution are difficult to be adsorbed by activated carbon,modified activated carbon(AC-N)was prepared by heat activated nitrogen doping method with coconut shell activated carbon as raw material and melamine as nitrogen source.The effects of initial pH of leaching solution,adsorption time,adsorption temperature,initial mass concentration of gold,Na_(2)S_(2)O_(3) concentration,S_(4)O_(6)^(2-) concentration and main metal ions on the adsorption of Au(S_(2)O_(3))_(2)^(3-) by AC-N were investigated.The results show that the adsorption capacity of AC-N on Au(S_(2)O_(3))_(2)^(3-) firstly increases and then decreases with the increase of pH and temperature.Under the condition of the initial gold concentration of 20 mg/L,the adsorption capacity reaches the maximum.Because Na_(2)S_(2)O_(3) is easily decomposed by oxidation,the product S_(4)O_(6)^(2-) has passivation effect on gold,and the adsorption of AC-N is inhibited with the increase of concentration.The adsorption capacity firstly increases and then decreases with the increase of Cu^(2+),Pb^(2+)and Zn^(2+)mass concentration.In the presence of NH_(3),Cu(NH_(3))_(4)^(2+) can be formed with Cu^(2+)to reduce the consumption of Na_(2)S_(2)O_(3).The adsorption kinetics results show that the adsorption of Au(S_(2)O_(3))_(2)^(3-) by AC-N is a fast and then slow process,and the adsorption reaches saturation after 30 h.The adsorption process conforms to the quasi-first order kinetic model,which indicates that the adsorption rate is controlled by both surface liquid film diffusion and intra-particle diffusion.